Loans, Leases and Other Real Estate - Composition of Company`s Loan and Lease Portfolio (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 4,228,052	$ 4,156,680
Less: deferred fees	(4,083)	(3,960)
Loans and leases, net of deferred fees	4,223,969	4,152,720
Commercial, secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	2,885,997	2,831,184
Commercial, industrial and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	339,665	340,400
Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	78,238	75,039
Real estate - residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	323,054	322,880
Real estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	283,378	264,908
Home equity and consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 317,720	$ 322,269